Process



Patented Aug. 7, 1951 I rRooEssFoR THE. MANUFACTURE or zINo PEROXIDE -William Stanley Wood, Harpenden, and George Clennett,;Luton, England, assignors-to Laporte -Chemicals;Limited, a British company 'No Drawing. Application January 25, 1947, "Serial No. 724,458. In Great Britain February 4,

1946 .10 Claims.

ilhisi-inventionrelates to axprocess for themati- Two .main processes have been previously proposed forithe .manuiacture of zinc peroxide. In thefirst-ofathese zinc oxideiwas mix-ed'with con.- :centrated hydrogen "peroxide to form .a paste which "wasathen dried. If a higher content of active oxygen 'wasme'quired thedried product was treated several :times .with' hydrogen peroxide. Such :.a process, .however, gives a low oxygen efficiency and presents dimcultiesin producing the maximumoxygen content inthe finished product. Also owing to the considerable handling of the product the process. is time-consuming and unsuitable for large scale production. In the second main process an alkaline solution of a zinc salt Was precipitated with hydrogen peroxide. The resultant peroxide, however, is slimy and difficult to filter one large scale and the product is not stable.

It is an object ofthe present invention to provide :animproved processior the manufacture of zinc peroxide having certain advantages :hereinafter referred to.

With this object in view the present invention provides a process for the manufacture of zinc peroxide wherein zinc oxide or zinc hydroxide is added inseveral portions to a solution of hydrogen peroxide containing an acid which forms a water-solublesalt with zinc oxide or zinc hydroxide or a water-soluble zinc salt to give .a precipitate of zinc peroxide the amount of each portion added being small in comparison with the total of the hydrogen peroxide measured molecularly.

As acid We prefer to use hydrochloric "acid, nitric acid or sulphuric acid and we prefer to add 2 to 25 gms. of acid or water-solubl zinc salt per litre .of the hydrogen peroxide solution.

The zinc oxide or zinc hydroxide and the hydrogen peroxide are preferably present in equimolecular proportions since an excess of hy-- drogen peroxide leads to a loss in oxygen efiiciency.

We prefer .to use .a ratio of zinc oxide to solution of from 1:3 to 1:7 or a corresponding ratio of zinc hydroxide. This'of course depends on the hydrogen peroxide concentration, i. e. the higher the hydrogen peroxide concentration the higher the ratio of solid to liquid.

It was found that :it is advantageous to have a certain amount of acid which forms a watersoluble salt with zinc. .oxideor ,zinc hydroxide or water-soluble :zinc salt. present in the hydrogen peroxide solution; When the acid is present this dissolves some ofthe zinc oxide'or zinc hydroxide and when this is precipitated as :zinc .perioxide, the acid is liberated- The acid or water-soluble zinc salt thus serves to initiate and catalyse the reaction. i r i Thus the probable course 0f :the reaction in the case of sulphuri'ciacid is that .the acid first attacks the :zinc oxide:

V 'ZnO-i-HZSO4=fZnSO4+HzO (11) Thehydrogen peroxide then reacts with the zinc sulphate:

ZHSO'4+H202FZI1 O2 Ti d-12504 (2) Thus the acid is "regenerated and'reac'tion (1') again takesp'lace; In the case 'of the additiono'f a water soluble zinc salt the reactions are the same but presumably reaction -(2') takes place first. The process "of "the present invention -is preferably conducted "at an increased temperature as this results in "a product of a satisfactory granular nature. The beneficial action of the acid is also most marked at an increased temperature. Thus we do not cool the reaction vessel but allow the temperature to be increased by the heat ofthe reaction. The "reaction is preferably conducted at above 30C. but the temperature should not he allowed to rise above Chewing to decomposition. The reaction can for example he conducted at 50 C. with th zinc peroxide'slurry cooled to 35 C. for filtration to preventoxygen loss"during-this'process.

The process is preferably conducted with =hydrogen peroxide "solutions of such concentration that the heat generated by the reaction is sum-- cient to raise the temperature of the reaction mixture to the preferred point. If the solutionis too concentrated the temperature will be too high and @if toodilute insu'mcient heat willbe available. Also the more dilute the hydrogen peroxide solution the more liquor there is to handle. while if the concentration :of the solution of hydrogen peroxide is too high the resulting :slurry will he too thick to handle.

It wasiound that a satisfactoryran'ge of concentration :of the hydrogen peroxide is from about. to 15% by weight =e. g.12%. .The temperature can be controlledito a certain extent by the rate of addition of the zinc oxide or zinc hydroxide to the hydrogen peroxide. it Although the process of thepresent invention can be conducted satisfactorily without the presence of stabiliserin thereaction it was found that the 'additi'onkof such a stabiliser improved the stability of thefinished product. ,For ex mother liquor shows a negligible quantity of hydrogen peroxide.

When the reaction is completed as shown by the absence of hydrogen peroxide in the mother liquor the zinc peroxide is filtered off, washed free from soluble salts, and dried. A granular stable product is 'obtained and this may be ground in a suitable mill if a finer product is required.

The process of the present invention has a number of advantages. Thus it reduces the amount of material to beha'ndled, no external heat and very little cooling is required, the losses due to decomposition are reduced to a minimum and the properties and stability of the finished product are satisfactory in every respect.

The following examples illustrate how the process of the invention may be carried into effect:

1. 120 gals. of water were mixed with 896 lbs. of hydrogen :peroxide (27.6% by weight) to give 2096 lbs. of a solution containing 11.8% of hydrogen peroxide. To this solution lbs. of concentrated sulphuric acid was then added.

'600 lbs. of zinc oxide was then added to the above solution in 6 equal additions at approximately 5-minute intervals. At the end of the additions the temperature ofthe reaction mixture was. 51 C. An addition of 1.75 lbs. of sodium silicate (78 Tw. Na2O2SiO2=1:3.4) was then made to the reaction mixture. The mixturewas then cooled to 35/40 C. and the zinc peroxide was separated in a centrifuge.

The zinc peroxide pulp was washed free from soluble sulphates, removed from the centrifuge and dried at 90-100 C. for 6 hours.

The final yield was 760. lbs. of zinc peroxide containing 66.2% of ZnOz. The oxygen efficiency was 71%.

2. 29 gals..of water were mixed with 232 lbs. of hydrogen peroxide (27.6% w./w.) to give 522 lbs. of a solution containing 12.4% by wt. of hydrogen peroxide. To this solution 7 lbs. of concentrated nitric acid (8. O. 1.42)' was then added. 7

150 lbs. of zinc oxidegwas then added in five equal additions at approximately 5 minute intervals. After the additions the temperature of the reaction mixture was 34 C. An addition of 3.5 lbs. of sodium silicate (78 Tw. Na2O:SiO2=- 1:3.4) was then made to the reaction mixture. The mixture was then cooled to 28 C. and the zinc peroxide removed in a centrifuge.

The zinc peroxide was washed free from soluble salt, removed from the centrifuge and dried at 100 C. for 5 hours.

The yield was 190 lbs. of zinc peroxide containing 62.0% of Z1102. The oxygen emciency was 65%.

3. 29 gals. of water were mixed with 232 lbs. of hydrogen peroxide (27.6% w./w.) to give 522 lbs. of a solution containing 12.4% w./w. of hydrogen peroxide. To this solution 5.0 lbs. of zinc nitrate was added. 1

150 lbs.'of zinc oxide was" then added to the above solution in five equal additions at approximately 5'minute intervals. At the end of the additions the temperature of the reaction mixture was 36 C. An addition of 3.5 lbs. of sodium silicate (78 Tw. NazO:SiO2'=1:3.4) was then containing 66.5

made to the reaction mixture. The mixture was then cooled to 32 C. and the zinc peroxide was removed by centrifuging.

The zinc peroxide pulp was washed free from soluble salts, removed from the; centrifuge and dried at 100 C. for 5 hours. j; f I

The final yield was 189 lbs. of zinc peroxide of ZnOz. The oxygen efiiciency was 68.9%.

The total oxygen efficiency given in the examples is calculated on the Z1102 yields only and takes no account o f the residual oxygen in the mother liquor.

We claim: 1

1. A process for. the manufacture of zinc peroxide which comprises reacting hydrogen peroxidein a 1'0tof15% by weight aqueous solution containing 2 to 25 grams per liter of a substance selected from the group consisting of water-soluble zinc salts and acids which form watersoluble zinc salts with a zinc compound selected from the group consisting of'zinc oxide and zinc hydroxide at a temperature in the range. of about 30-70 C. to produce a granularprecipitate of zinc peroxide, the zinc compound being added in several portions-each of .which is small in comparison with the total of the hydrogen peroxide present in said solution and the intervals between successive additions being regulated so as to keep the temperature in the reaction zone below about 70 C. r

. 2. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group'consisting of zincoxide andzinc hydroxide to a 10 to 15 by Weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. per liter of solution of a substance selected from the group consisting of water soluble zinc salts and acids which form water soluble zinc salts, said zinc compound being added in several portions each oflwhich is small in comparison with the total of the hydrogen peroxide present in said solution, and controlling the rate of addition of said portions so as to maintain the temperature of the reaction mixture below about 70 C., thereby forming a granular precipitate of zinc peroxide.

3. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a 10 to 15%" by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. of hydrochloric acid per liter of solution while maintaining the tempera ture in the range 30-70" C., said zinc compound being added in several portions each of which is small in comparison witlithe' total of the hydrogen peroxide present in-saidsolution, andcontrolling the'rate of addition of said portions so as to maintain the temperature of the reaction mixture below about 70 C., and thereby producing a granular precipitate of zinc peroxide.

'4. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consistingof zinc oxide and zinc hydroxidetoa 10 to "15% by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. of sulphuric acid per liter of solution while maintaining the temperature in the range 30-70 C., said zinc compound being added in several portions eachof which is small incomparison' with the totalof the hydrogen peroxide present in said solution, and controlling the rate of addition of said portions so as to maintain the temperature of the reaction mixture below about 70 C., and thereby producing a granular precipitate of zinc peroxide.

5. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a to by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. of nitric acid per liter of solution while maintaining the temperature in the range 30-70 0., said zinc compound being added in several portions each of which is small in comparison with the total of the hydrogen peroxide present in said solution, and controlling the rate of addition of said portions so as to maintain the temperature of the reaction mixture below about 70 0., and thereby producing a granular precipitate of zinc peroxide.

6. A process for the manufacture of zinc peroxide which comp-rises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a 10 to 15% by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. per liter of solution of a substance selected from the group consisting of water soluble zinc salts and acids which form water soluble zinc salts, while maintaining the temperature in the range 30-"l0 C., said zinc compound being added in several portions each of which is small in comparison with the total of the hydrogen peroxide present in said solution and said additions being so spaced as to maintain the temperature of the reaction mixture below about 70 C., and continuing said additions until the proportion by weight of zinc compound calculated as zinc peroxide equals from one-third to one-seventh of the weight of the solution, thereby producing a granular precipitate of zinc peroxide.

7. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a 10 to 15% by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. of hydrochloric acid per liter of solution, while maintaining the temper- A ature in the range 30-'70 C., said zinc compound being added in several portions each of which is small in comparison with the total of the hydrogen peroxide present in said solution and said additions being so spaced as to maintain the temperature of the reaction mixture below about 70 0., and continuing said additions until the proportion by weight of zinc compound calculated as zinc peroxide equals from one-third to oneseventh of the weight of the solution, and thereby producing a granular precipitate of zinc peroxide.

8. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a 10 to 15% by weight aqueous solution of hydrogen peroxide containof solution, while maintaining the temperature in the range 30-70 0., said zinc compound being added in several portions each of which is small in comparison with the total of the hydrogen peroxide present in said solution and said additions being so spaced as to maintain the temperature of the reaction mixture below about C., and continuing said additions until the proportion by weight of zinc compound calculated as zinc peroxide equals from one-third to one-seventh of the weight of the solution, and thereby producing a granular precipitate of zinc peroxide.

9. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a 10 to 15% by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. of nitric acid per liter of solution, while maintaining the temperature in the range 30-70 C., said zinc compound being added in several portions each of which is small in comparison with the total of the hydrogen peroxide present in said solution and said additions being so spaced as to maintain the temperature of the reaction mixture below about 70 C., and continuing said additions until the proportion by weight of zinc compound calculated as zinc peroxide equals from one-third to one-seventh of the weight of the solution, and thereby producing a granular precipitate of zinc peroxide.

10. A process for the manufacture of zinc peroxide which comprises adding a zinc compound selected from the group consisting of zinc oxide and zinc hydroxide to a 10 to 15% by weight aqueous solution of hydrogen peroxide containing from 2 to 25 gms. per liter of solution of a substance selected from the group consisting of water soluble zinc salts and acids which form water soluble zinc salts, so controlling the rate of addition of the zinc compound as to maintain the temperature in the reaction zone between 30 and 70 C., and continuing said additions until the proportion by weight of zinc compound calculated as zinc peroxide equals from one-third to one-seventh of the weight of the solution, and thereby producing a granular precipitate of zinc peroxide.

WILLIAM STANLEY WOOD. GEORGE CLENNETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,304,104 Klabunde et a1. Dec. 8, 1942 2,393,891 Dawsey et a1 Jan. 29, 1946 OTHER REFERENCES Mellors, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 4, pages 530, 531, 613, 614. Longmans, Green & 00., N. Y., publishers. 

10. A PROCESS FOR THE MANUFACTURE OF ZINC PEROXIDE WHICH COMPRISES ADDING A ZINC COMPOUND SELECTED FROM THE GROUP CONSISTING OF ZINC OXIDE AND ZINC HYDROXIDE TO A 10 TO 15% BY WEIGHT AQUEOUS SOLUTION OF HYDROGEN PEROXIDE CONTAINING FROM 2 TO 25 GMS. PER LITAER OF SOLUTION OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF WATER SOLUBLE ZINC SALTS AND ACIDS WHICH FORM WATER SOLUBLE ZINC SALTS, SO CONTROLLING THE RATE OF ADDITION OF THE ZINC COMPOUND AS TO MAINTAIN THE TEMPERATURE IN THE REACTION ZONE BETWEEN 30 AND 70* C., AND CONTINUING SAID ADDITIONS UNTIL THE PROPORTION BY WEIGHT OF ZINC COMPOUND CALCULATED AS ZINC PEROXIDE EQUALS FROM ONE-THIRD TO ONE-SEVENTH OF THE WEIGHT OF THE SOLUTION, AND THEREBY PRODUCING A GRANULAR PRECIPITATE OF ZINC PEROXIDE. 